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Last fall, Andrea wrote an excellent piece on prions, and how they “contradict century-old biological assumptions and seem to defy the expectations of Darwinian evolutionary theory.” He gives an overview of prions and discusses their potential role in heredity. My interest in them, of course, comes from the diseases they cause. Over at Aetiology, I have a post up discussing a new Lancet paper on the prion disease, kuru, and its potential to act as a model for other human prion diseases (such as “mad cow”). The authors suggest two things: one, that the incubation period of so-called “mad cow” disease may be longer than previously thought, and two, that there may be “waves” of epidemic, determined partly by host genetics.

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Are there still some that maintain that prions do not contain a nucleic acid genome?

Are there some that maintain that prions do contain a nucleic acid genome?

This is from the Andrea Bottaro article linked at the top of this page:

Prions are unlike any other infectious agent in that they seem to have no nucleic acids at all. Indeed, after a long controversy, most scientists currently agree that prions propagate entirely as alternatively folded forms of certain proteins, through a mechanism that resembles crystal nucleation

I’m curious —- are there any indications that prions, when they reproduce, are capable of changing and then reproducing those changes?

There certainly are different “strains” of prions, that is, alternatively folded prionic forms of the same protein (they also have different propagation properties - “fitness” if you will). I am not sure if one prion strain can spontaneously “mutate” into another, although that might perhaps be possible at some low rate, just like a normal protein can on occasion misfold spontaneously into a prion.

I am not sure if one prion strain can spontaneously “mutate” into another, although that might perhaps be possible at some low rate, just like a normal protein can on occasion misfold spontaneously into a prion.

I’m not sure either, and that’s what I’m asking.

If a prion can indeed spontaneously mis-fold into another form, and then that form gets copied, and then passed on to another host, where it can also mis-fold again, and pass on THAT copy, then it would seem reasonable that some foldings would be more efficient than others. I.e., there would be replication, mutation, selection, and reproduction of the selected mutations. NASA’s definition of “life”.

If a prion can indeed spontaneously mis-fold into another form, and then that form gets copied, and then passed on to another host, where it can also mis-fold again, and pass on THAT copy, then it would seem reasonable that some foldings would be more efficient than others. I.e., there would be replication, mutation, selection, and reproduction of the selected mutations. NASA’s definition of “life”.

It’s interesting to consider whether prions can really be said to replicate. They certainly don’t do so in the conventional sense that DNA or a virus does. A mis-folded prion protein can only ‘replicate’ by inducing an existing, normally-folded protein molecule to become mis-folded. (Sort of like Vonnegut’s Ice-9.)

Without a source of the normally-folded protein, the prion can’t propagate. On the other hand, essentially every current living replicator requires a pre-existing source of biological molecules, so maybe there’s no real distinction.

If a prion can indeed spontaneously mis-fold into another form, and then that form gets copied, and then passed on to another host, where it can also mis-fold again, and pass on THAT copy, then it would seem reasonable that some foldings would be more efficient than others. I.e., there would be replication, mutation, selection, and reproduction of the selected mutations. NASA’s definition of “life”.

Crystals also replicate off a template. This is the basis of Cairns-Smith Genetic Takeover: crystals too would misform, and some errors by chance would be superior at replicating.

Theoretical biologists and philosophers of science have defined what’s necessary for evolution by natural selection in abstract terms. Roughly speaking, any imperfect replicator whose copies are more or less likely to replicate themselves will evolve.

If creationists were going after germ theory the way they’re going after evolutionary theory, prions would be a very good example of something that “challenges the orthodoxy” or “deals a fatal blow to a seriously weakened theory” or whatever else it is that creationists are so fond of claiming.

Which just goes to show that creationists aren’t bothered about challenges to specific aspects of theories unless the theories happen to be in current conflict with their theology.